Lifting magnet



June 3, 1958 K. A. BLIND 2,837,702y

LIFTING: MAGNET Filed Nov; 1'7, 1955 IN V EN TOR reiterated une a, llo-.ns

LIFTIN G MAGNET Karl A. lilind, fhiensville, 'W

Application November 17, i955, Serial No, 547,379

2 Claims, (Ci. S17-164) The present invention relates generally to improvements in magnets for handling diverse magnetic materials, and relates more specifically to improvements in the construction and :operation of electrically energized lifting magnets of the movably suspended type.

The primary object of my invention is to provide an improved electric lifting magnet in which the energizing coil assemblage is amply protected `against: possible short circuiting and other damage.

lt has long been common practice to utilize electrically energized and movably suspended lifting magnets of the type having a group or stack of annular pancake windinseparated by layers of insulation providing an energizing coil conned within an annular recess of the magnet body, for the purpose of lifting, lowering or transportirnT diverse magnetic materials from place to place. The pancake windings of these mavnets are ordinarily formed of spirally wound copper strips, and the insulation layers heretofore applied 'between the windings `consisted of mica or asbestos and a binder such as sliellac or the like for holding the insulating ingredients together so 4as to provide compressible or elastic sheets intended to compensate for transverse expansion and contraction of the windings. Depending upon the magnetic force required, the number of windings in each stack may be varied considerably, and under severe operating conditions the windings become heated to temperatures sufficiently high 'to rapidly deteriorate and break down these prior elastic insulation layers thereby loosening and frequently damaging the energizing coils.

lt is therefore an important object of the present invention to eliminate such destructive action of the insulation and resultant damaging of the energizing coils of these magnet assemblages, primarily by providing means in addition to or other than the insulation layers for more effectively compensating for transverse expansion and contraction of the pancake windings.

Another important object of this invention is to provide simple but reliable instrumentalities for enhancing the efficiency and durability of electrically energized lifting magnets of the pancake winding type.

A further important object of the invention is to provide an improved energizing coil assemblage for magnets or the like, wherein the annular windings are insulated from each other by non-hygroscopic intervening layers of material which will not soften or deteriorate in the presence of moisture.

Still another important object of my invention is to provide improved mechanism for automatic lly maintaining the several coil windings of a lifting magnet snugly couiined and well insulated against possible short circuiting under most severe operating conditions.

These and other more specific objects and advantages of the present invention will be apparent from the following ldetailed description.

A clear conception of the features constituting the present improvements and of the construction and operation of a typical electric lifting magnet embodying the invention, may be had by referring to the drawing accompa u ing and forming a part of this specification in which like reference characters designate the same or similar parts in the various views.

Fig. l is a transverse vertical section through an improved electrically energized lifting magnet of the pancake winding type, the section having `been taken along the irregular line l--i of Fig. 2;

Fig. 2 is a bottom View of the lifting magnet illustrated in Fig. l, showing the location of the improved coil cX- pansion and `contraction compensating elements; and

Fig. 3 is an enlarged central vertical section through an improved spring assembly especially adapted for use in a lifting magnet such as shown in Figs. l and 2.

While the invention has been shown and described herein as having been embodied in an electrically encrgized lifting magnet having therein a stack of eight annular pancake windings, it is not the intent to restrict its use to a magnet of this type having a specific number of such windings; and it is also contemplated that specific descriptive terms employed herein be given the broadest possible interpretation consistent with the actual disclosure.

Referring to the drawing, the powerful universally movable lifting magnet shown, comprises in general, a circular body 4 of magnetic material having therein an annular recess 5 and being provided with annular outer and inner magnetic pole shoes 6, '7 respectively of magnetic material coacting with a non-magnetic closure disn t 'ind which are firmly secured to the body Il; `a supe niposed group or stack of annular windings 9 forming energizing coil confined within the body recess il ydisc S and being separated from each other `by annular layers l() of insulation; an annular pressure plate ll slidably confined within the recess S and coaeting with the upper or innermost winding 9 of the stack; and several annular sets of resilient elements or springs i2 con t within sockets 13 and interposed between the pressure plate 1l and the body 4.

The circular body i is ordinarily formed of steel and is provided at its top with suspension ears l5 and pins i6 with which chains i7 are adapted to cooper so to support the magnet assemblage for free movement my direction, and the energizing Coil is adapted to receive electric current through a exible cable 'L in a well known manner. The annular pole shoes 6, 'i' which normally clamp the sealing disc in closed position, may be fastened to the body as by screws and bolts T disc S may be formed of manganese r any other suitable non-magnetic material. T he pancake windings S' constructed of spirally wound copper strip and are coniined within the body recess 5 by tne closure disc il, and the periphery of the coil is surrounded by granular filling compound 26, Ias shown in l? l.

ln accordance with the present invention, the insulation layers 10 which are interposed between the lower winding 9 and the disc S, between the adjacent windings 9, and between the upper winding 9 and the pressure plat-e are formed of any non-compressible and non-hygroscoiic solid insulating substance such as silicon bonded by fiore glass, so that these layers itl will not be detrimentally aiected by pressure or moisture. The annular pressure plate 11 should `be formed of relatively thick and sturdy metal plate and is preferably provided with bronze ceT tral bushing Z2 and with a peripheral `.Tl-ring Z3 slidab.,Y but sealingly engaging the concentric walls of the anni body recess 5. The resilient elements or springs l2 should l e relatively stili and spaced to produce uniform pressure against and throughout the en" e area of the plate ll, so that all of the coil windings 9 and the insulation layers lil will be constantly subjected to constant lateral pressure.

While the resilient spring elements l2 may be of any suitable type, it is preferable te construct these cpriugs LAD Q as shown in detail in Fig. 3, v'herein each unit comprises a stack of alternately disposed disks 25, 2d. The disks 25' have resilient medial areas 2,7 while the alternate disks 2o have resilient peripheries 23, so that when end pressure is applied to the stack the resilient portions 27, 2.3 of the two sets of disks 25, 26 will be deflected by the thicker areas of the adjacent disks but will return to normal position whenever this pressure is released.

When the improved lifting magnet has been properly constructed and assembled as above described, it may be suspended from a hoisting and lowering device with the aid of the chains f7 and electric current from any suitable source may be supplied to energize the coil through the flexible cable 13, in a well known manner. When the magnet has been thus energized the pole shoes 6, v bebrought into close proximity with magnetic material or articles which are to be lifted, and as the latter enter the magnetic iield bridging the ylower sealing ydisc 8, they will be attracted and will `cling to the magnet assemblage until the energizing current is interrupted and the magetic field has been disbursed.

Whenever the magnet is being actuated with high intensity as when handling heavy loads, the pancake windings 9 will become heated and will expand or increase in lateral thickness, and since the insulation layers are incompressible such expansion of the coil can only be compensated for by movement of the pressure plate il along the recess 5 and away from the fixed sealing disc d. This movement of the pressure plate il compresses the springs l2 which exert uniform pressure throughout the area of the plate il, and when the energizing current is reduced the windings 9 will gradually cool and contract, whereupon the compressed springs l2 expand and move the pressure plate il in the opposite direction toward the disc S so as to again compensatefor shrinkage of the net energizing coil. During such movement of the pressure plate li, the central bushing 22 and the peripheral O-ring seal `effectively guide this plate along the concentric cylindrical bounding surfaces of the recess 5 and also prevent granular compound 2i) from entering the space above the pressure plate, and this space may be vented to the ambient atmosphere through the opening at the right of Fig. l which permits insertion of the energizing current conductors.

From the foregoing detailed description of the construction and functioning of the improved lifting magnet assemblage, it should be apparent that the present invention in fact provides a structure which protects the energizing 'coil 'against deterioration, and which also automatically compensates for expansion and contraction of the windr ings 9 due to variations in energizing current intensity. The use of incompressible and non-hygroscopic material in the formation of the insulating layers lil is importan in preventing excessive thinning of these layers due to the application of excessive pressure, and in valso avoiding possible deterioration due to the presence of moisture; and the formation of the pressure plate lll and the disposition .of the spring elements l2 insures the application of uniform pressure against the windings 9 throughout their entire areas at all times. However, the present improved safety device may also be advantageously applied to lifting magnets embodying the usual compressible insulation layers, and it may also be applied to old or new (E il 4 lifting magnet units of various capacities having any desited number of windings. It is also to be noted that the pressure plate il constitutes a part of the magnetic circuit despite the use of a non-magnetic guiding bushing 22, so that this plate l1 does not enhance the total weight of the magnet.

While various kinds of resilient elements or springs l2 may be utilized, the improved composite spring assemblage shown in Fig. 3 is especially well adapted for the required service, since it will retain its resiliency substantially constant for an indefinite period of time, and the resiliency of all such spring assemblages will also be uniform if the disks 25, 26 are properly constructed. Such an assemblage is also less subiect to breakage than when helical wire compression springs are employed.

lt should be understood that it is not desired to limit this invention to the exact details `of construction and operation of the lifting magnet assemblage herein specifically shown and described, for various modifications within the scope of the appended claims may occur to persons skilled in the art.

I claim:

1. In an electric lifting magnet, a magnetic body having adownwardly open recess bounded by coaxial annular inner and outer surfaces and a top surface, a stack of annular magnet energizing windings within said recess snugly embracing said inner surface but spaced from said outer surface and being separated by intervening incornpressible layers of insulation and surrounded by granular material, means coacting with the lowermost winding of the stack to retain the coil within said recess, a plate bearing against the uppermost winding 4of the stack and sealingly but slidably engaging both of said recess side surfaces, and an annular series of springs interposed between said top recess surface and said plate and coacting with the latter to compensate for expansion and contraction of said windings transversely of said insulation layers.

2. In an electric lifting magnet, va magnetic body having a downwardly open recess Vbounded by lcoaxial annular inner and outer surfaces and a top surface, a stack of annular magnet energizing windings Within said recess snugly embracing said inner surface but spaced from said outer surface and being separated -by intervening incompressible layers of insulation and surrounded by granular material, means coacting with the lowermost winding of the stack to retain the coil within said recess, an annular pressure plate bearing against the uppermost winding of the stack and sealingly engaging both of said recess side surfaces but being slidable therealong, and an annular series of uniformly spaced compression springs interposed between said top recess surface and said pressure plate and coacting with the latter to compensate for expansion and contraction of said windings transversely of said insulation layers.

References Cited in the file of this patent UNITED STATES PATENTS 1,255,947 Thordarson Feb. l2, 1918 1,532,449 Sederholm Apr. 7, 1925 FOREIGN PATENTS 648,697 Great Britain V. Oct. 9, 1947 

